Cellular communication systems continue to grow in popularity and have become an integral part of both personal and business communications. Cellular telephones allow users to place and receive phone calls most anywhere they travel. Moreover, as cellular telephone technology has increased, so too has the functionality of cellular devices. For example, many cellular devices now incorporate Personal Digital Assistant (PDA) features such as calendars, address books, task lists, calculators, memo and writing programs, etc. These multi-function devices usually allow users to wirelessly send and receive electronic mail (email) messages and access the internet via a cellular network and/or a wireless local area network (WLAN), for example.
As the functionality of cellular communications devices continues to increase, so too does the demand for smaller devices that are easier and more convenient for users to carry. As any circuit board and electronic components thereon are reduced in size and placed closer together, including antenna and microphone components, various electronic components can pick up energy and create interference within the system. For example, an internal surface mounted microphone could pick up energy directly from a power amplifier or from the radiated energy emitted by an antenna. This unwanted reception of energy from respective power amplifiers and antennae may be particularly problematic in a packet burst transmission as part of a Global System for Mobile communications (GSM) system, including the 450 MHz, 900 MHz, 1800 MHz and 1900 MHz frequency bands.
Other interfering signals can be generated when the liquid crystal display (LCD) in some mobile wireless communications devices radiates radio frequency (RF) interfering energy and degrades receiver sensitivity. This may be problematic where the interfering energy is generated by the microprocessor or central processing unit (CPU) of a wireless mobile communications device and fed into the LCD lines, along with interfering energy generated by the LCD itself. Other problems may occur when the interfering radio frequency (RF) energy is coupled to the mobile wireless communications device causing audio break through tests to fail for both the uplink and downlink. Even the keyboard circuits can create unwanted interference problems. For example, the radio frequency receiver sensitivity is often degraded by the electromagnetic interference (EMI) of digital harmonics from the microprocessor or CPU via the keyboard because of the resulting loop formed by any keyboard circuits. In some instances, strong RF energy, for example, such as the transmitted power from the radio via the antenna interferes with or couples to the microprocessor or CPU input/output (I/O) lines of a mobile wireless communications device through the keyboard Key-In and Key-Out lines and causes a reset of the microprocessor or CPU.
A shielding container can protect components on a printed circuit board (PCB), preferably for a cellular phone, against interference from other components due to electric fields. A shielding container covers a number of electronic components on a printed circuit board, and thereby protects these components from disturbing other electronic components on the printed circuit board. The use of shielding containers is well known because GSM phones have printed circuit boards equipped with different components that may disturb each other if they are not shielded from each other.
A first type of shielding container includes one entire box shaped piece soldered onto the printed circuit board. This type of shielding container does not permit access to components covered by the shielding container, which makes it very difficult to repair or inspect any of the components covered or shielded by the shielding container. An alternative is having holes or apertures to let the heat in to solder the components at the same time as the shielding container.
A second type of shielding container includes two pieces, one frame and one lid. The lid is snapped onto the frame and can be removed from the frame, which is soldered onto the printed circuit board, to enable repairing or inspection of the components shielded by the shielding can. The second type may be attached to the printed circuit board in different ways. One way is to solder the frame onto the printed circuit board first and then attach the lid to the frame. Another way is to snap the lid onto the frame and solder the assembly onto the printed circuit board, but then there is a need for holes or apertures in the lid to let in the heat during soldering. Otherwise the components covered or shielded by the shielding container will not be properly soldered since the heat cannot reach the components. It is preferable to solder the frame with the lid attached to save work operations. However, according to the prior art there may be problems getting a good solder joint, when using a pre-joined shielding container.
U.S. Pat. No. 5,895,884 to Davidson is directed to a shielding device with a push fit lid. The shielding device is formed from two unitary pieces, one of which is a generally planar member taking the form of a lid and the other piece takes the form of a side wall member which is adapted for mounting to a substrate surface on which is mounted circuit elements. The two pieces together combine to create the shielding device for inhibiting the passage of electromagnetic radiation to and/or from a group of circuit elements. The lid may have flanges for connection onto the side wall member and the side wall member may have intersecting dividing walls disposed internally thereof.
U.S. Pat. No. 6,600,663 to Koleda is directed to a shielding can for a printed circuit which includes a frame with side walls and a lid with increased flexibility from slits on the sides of the lid. These slits enable a flexible contraction, when soldering the shielding can onto the printed circuit board.
U.S. Pat. No. 6,137,051 to Bundza is directed to an electromagnetic interference and compatibility (FMS/EMC) shielding enclosure for a printed circuit board (PCB) or other electronic components that has a conductive plastic top housing portion and a conductive bottom housing portion. The top housing portion has projecting fingers integral therewith. The bottom housing portion has an inner surface with walls projecting therefrom for substantially encompassing the PCB. When the enclosure is assembled, the PCB is located between the top housing portion and the bottom housing portion, the fingers from the top housing portion surround at least a major portion of the PCB and the fingers physically contact the bottom housing portion or are sufficiently close for capacitive coupling.
There is still a need for a handheld electronic device including a multi-compartment shielding container with inter-compartment shielding and sufficient stiffness to be used for printed circuit boards within the electronic device.